Connie, your condition should be considered "normal".
Because of the tinning/plating processes and potential interaction with
materials or heat stress at the points leads enter the component, there
is typically about 0.050 in "unknown" space from the edge of wettable
surface to the component body. In fact, J-STD-002 does NOT require
wetting in this 0.050 in space.
It will be a rare and exceptional instance where the exposed copper will
introduce a failure mechanism, whether it's at the edges of your
conductors (traces--look at them), cut ends of leads, or unplated area.
In fact, Rev D for 610 has modified this wording to remove the reference
to exposed copper as a result of lead damage. Lead damage is separate
criteria and anything greater than stated limits is a defect. It doesn't
matter if it exposes basis metal.
Clause 5.2.1 intro from A-610D:
Component leads, sides of land patterns, conductors, and use of liquid
photoimageable solder resist, can have exposed basis metal per original
designs.
Some printed circuit board and conductor finishes have different wetting
characteristics and may exhibit solder wetting only to specific areas.
Exposed basis metal or surface finishes should be considered normal
under these circumstances, provided the achieved wetting characteristics
of the solder connection areas are acceptable.
Acceptable - Class 1,2,3
* Exposed basis metal on:
* Vertical conductor edges.
* Cut ends of component leads or wires.
* Organic Solderability Preservative (OSP) coated lands.
* Exposed surface finishes that are not part of the required solder
fillet area.
Acceptable - Class 1
Process Indicator - Class 2,3
* Exposed basis metal on component leads, conductors or land surfaces
from nicks or scratches provided conditions do not exceed the
requirements of 7.1.2.3 for leads and 10.2.9.1 for conductors and lands.
<7.1.2.3 and 10.2.9.1 are lead/conductor damage clauses>
You'll note that exposed basis metal in 610D does NOT lead to a defect
condition.
Jack Crawford, IOM
IPC Director Certification and Assembly Technology
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NEW PHONE 847-597-2893
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Connie Korth
Sent: Thursday, December 09, 2004 8:59 AM
To: [log in to unmask]
Subject: [TN] copper exposed
Good AM Techies,
We have some resistors that did not take the tinning all the way
to the body. There is some copper exposed by the body, but the lead in
the solder connection is good. Per IPC-610, if copper is exposed due to
deformation or nicks/gouges >10%, it is a defect. We have absolutely no
deformation in these component leads. My decision was to leave them in
the board. We have a Mfg. Engineer who wants to have them all replaced.
He feels I have interpreted the IPC-610 incorrectly. I feel that this
is unnecessary rework that could damage the PCB. Any supporters out
there?
Connie M. Korth
Quality Specialist
Reptron Manufacturing Services, Hibbing
[log in to unmask]
218.262.8209
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